1. Technical Field
The present invention relates to a fuel injection apparatus of an internal combustion engine which has a diagnostic function to detect an air-fuel ratio fault, and more particularly relates to the fuel injection apparatus which can suitably diagnose the air-fuel ratio fault, even if a fuel injection amount is corrected to increase.
2. Related Art
A fuel injection apparatus provided in, for example, a gasoline engine for a passenger car has a self-diagnostic function which compares a value (for example, an actually measured lambda λ) related to an air-fuel ratio detected by an air-fuel ratio sensor or the like provided in an exhaust pipe, with a given threshold value, and which determines a fault in which an air-fuel ratio is excessively rich or lean. Such a self-diagnostic function should be configured to prevent misdiagnosis, even if the properties of the supplied fuel varies due to variations of fuels distributed in the market.
For example, Japanese Unexamined Patent Application Publication (JP-A) No. 2010-1846 discloses that a diagnostic apparatus for an internal combustion engine that can utilize gasoline and alcohol mixed-fuel has a function which estimates the concentration of alcohol in the mixed-fuel and utilizes a stored value of the concentration of alcohol estimated during the former trip immediately after starting the engine.
Generally speaking, during a cold period and a cold temperature period, in which fuel is difficult to vaporize, in order to ensure fuel ignition and fuel stability even if fuel of relatively low volatility is supplied, a fuel injection amount is corrected to increase during a warm period (after warm-up) and thus the air-fuel ratio is likely to be rich. However, in the case where relatively volatile fuel is supplied and increasing correction is performed, the air-fuel ratio detected by an air-fuel ratio sensor or the like becomes excessively rich. As a result, erroneous determination, in which the air-fuel ratio is abnormally rich, may be established despite the fact that the fuel injection apparatus itself is normal.
Thus, heretofore, the diagnosis is not carried out during the cold period when the increase value correction of fuel is performed and misdiagnosis might occur. Accordingly, even if a fault occurs in the fuel injection apparatus, a relatively long period is required to detect the fault after starting the driving.